Latest research in football - week 8 - 2014

#1 The health profile of football/soccer players in Northern Ireland - a review of the uefa pre-participation medical screening procedure
Authors: Heron N, Cupples M.
Reference: BMC Sports Sci Med Rehabil. 2014 Feb 13;6(1):5. [Epub ahead of print]
Summary: It is compulsory that domestic football/soccer teams in UEFA competitions organise players' pre-participation medicals. Although screening guidelines have been established, these remain controversial. The findings of medical examinations can have lasting consequences for athletes and doctors. No previous studies have reported UEFA pre-participation screening results in semi-professional footballers. This study aims to further knowledge regarding 'normal' data in this population. Retrospective audit and analysis of records of pre-season medicals for all male first-team players at one semi-professional Northern Ireland Premiership team between 2009-2012. Medicals were conducted by the club doctor following the UEFA proforma. Height, weight, blood pressure (BP), full blood count (FBC), dipstick urinalysis and resting electrocardiogram (ECG) were conducted by an independent nurse. Only one ECG must be documented during a player's career; other tests are repeated yearly. 89 medicals from 47 players (6 goalkeepers, 11 defenders, 22 midfielders and 8 attackers; mean age 25.0 years (SD 4.86)) were reviewed. Mean height of the players was 179.3 cm (SD 5.90) with a mean weight of 77.6 kg (SD 10.5). Of 89 urine dipsticks, 7 were positive for protein; all 7 were normal on repeat testing following 48 hours of rest. Of 40 ECGs (mean ventricular rate 61.2 bpm (SD 11.6)), one was referred to cardiology (right bundle branch block; prolonged Q-T interval). No players were excluded from participation. This study provides important information about 'normal' values in a population of semi-professional footballers. Urinalysis showing protein is not uncommon but is likely to be normal on repeat testing.


#2 Dynamic knee stability and ballistic knee movement after ACL reconstruction: an application on instep soccer kick
Authors: Cordeiro N, Cortes N, Fernandes O, Diniz A, Pezarat-Correia P.
Reference: Knee Surg Sports Traumatol Arthrosc. 2014 Feb 12. [Epub ahead of print]
Summary: The instep soccer kick is a pre-programmed ballistic movement with a typical agonist-antagonist coordination pattern. The coordination pattern of the kick can provide insight into deficient neuromuscular control. The purpose of this study was to investigate knee kinematics and hamstrings/quadriceps coordination pattern during the knee ballistic extension phase of the instep kick in soccer players after anterior cruciate ligament reconstruction (ACL reconstruction). Seventeen players from the Portuguese Soccer League participated in this study. Eight ACL-reconstructed athletes (experimental group) and 9 healthy individuals (control group) performed three instep kicks. Knee kinematics (flexion and extension angles at football contact and maximum velocity instants) were calculated during the kicks. Rectus femoris (RF), vastus lateralis, vastus medialis, biceps femoralis, and semitendinosus muscle activations were quantified during the knee extension phase. The ACL-reconstructed group had significantly lower knee extension angle (-1.2 ± 1.6, p < 0.021) and increased variability (1.1 ± 1.2, p < 0.012) when compared with the control group. Within the EMG variables, the RF had a significantly greater activity in the ACL-reconstructed group than in the control group (79.9 ± 27.7 % MVC vs. 49.2 ± 20.8 % MVC, respectively, p < 0.034). No other statistically significant differences were found. The findings of this study demonstrate that changes in ACL-reconstructed individuals were observed on knee extension angle and RF muscle activation while performing an instep kick. These findings are in accordance with the knee stability recovery process after ACL reconstruction. No differences were observed in the ballistic control movement pattern between normal and ACL-reconstructed subjects. Performing open kinetic chain exercises using ballistic movements can be beneficial when recovering from ACL reconstruction. The exercises should focus on achieving multi-joint coordination and full knee extension (range of motion). LEVEL OF EVIDENCE: III.


#3 Velocity based training of lower limb to improve absolute and relative power outputs in concentric phase of half-squat in soccer players
Authors: Ramírez JM, Núñez VM, Lancho C, Poblador MS, Lancho JL.
Reference: J Strength Cond Res. 2014 Feb 10. [Epub ahead of print]
Summary: The power production is force-velocity related. We hypothesized that speed based training of lower limb using half-squat can lead to absolute and relative power improvement in concentric movement, with a same external load. One group of 19 soccer players (age 24.4 yr, SD = 3.7 yr) participated in a pretest-posttest power training protocol, consistent in 2 training sessions per week during 10 weeks, targeted to work the leg power by performing half-squat with fixed external load (M = 71.7; SD = 5.4), at 65% of 1RM. Measurements of power (absolute -W-, and relative -W/kg-), force (N) and velocity (m/s) (mean and peak) were made from a concentric movement of a half-squat exercise with a fixed external load. The training protocol increased relative power (M = 47.5, SD = 47.5; p < .001) and absolute power (M = 169.2; SD = 95.5; p < .001). Also, number of repetitions (M = 2.9; SD = 2.4; p < .01), force (M = 66.6; SD = 36.7; p < .001) and velocity (M = .1; SD = .1; p < .001) were increased. However, only improved velocity was related to changes in absolute (r = .939; p < .001) and relative (r = .757; p < .001) power.  The speed based training, combined with moderate to high external load can lead to an improvement of absolute and relative power in concentric phases of half-squat in soccer players. This could be important for improving the performance of the players in the field.


#4 Analysis of cohesion and collective efficacy profiles for the performance of soccer players
Authors: Leo FM1, Sánchez-Miguel PA2, Sánchez-Oliva D1, Amado D1, García-Calvo T1.
Reference: J Hum Kinet. 2013 Dec 31;39:221-9. doi: 10.2478/hukin-2013-0085. eCollection 2013.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916931/pdf/jhk-39-221.pdf
Summary: The principal aims of the study were to define different profiles of cohesion and perceived efficacy in soccer players and to measure their differences in performance. The subjects were 235 soccer players in the under-18 category who played in the National League in Spain and 15 coaches whose ages ranged from 29 to 45 years. Diverse instruments to assess cohesion, perceived efficacy, and expectations of success were used in the study. Moreover, we measured playing time and performance. The results of the study proved the existence of four cohesion and efficacy profiles that presented significant differences in expectations of success, playing time, and performance. Furthermore, significant differences were found in the distribution of players in the teams as a function of performance. The main conclusion of this study is that soccer players with higher cohesion and collective efficacy levels belonged to teams that completed the season at the top-level classification. In contrast, athletes with low cohesion and collective efficacy usually played in unsuccessful teams. Coaches and sports psychologists are encouraged to promote both social and task cohesion and collective efficacy to enhance team performance.


#5 Does an in-Season 6-Week Combined Sprint and Jump Training Program Improve Strength-Speed Abilities and Kicking Performance in Young Soccer Players?
Authors: Marques MC1, Pereira A2, Reis IG3, van den Tillaar R4.
Reference: J Hum Kinet. 2013 Dec 31;39:157-66. doi: 10.2478/hukin-2013-0078. eCollection 2013.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916921/pdf/jhk-39-157.pdf
Summary: The aim of this study was to examine the effect of a six-week combined jump and sprint training program on strength-speed abilities in a large sample of youth competitive soccer players. It was hypothesized that the experimental training group would enhance their jumping and sprinting abilities. Enhancement of kicking performance was also hypothesized due to an expected increase in explosive strength established by a plyometric and sprinting regimen. Fifty-two young male soccer players playing at the national level (aged 13.4 ± 1.4 years, body mass 53.4 ± 11.7 kg, body height 1.66 ± 0.11 m) took part in the study. Half of the group underwent the plyometric and sprint training program in addition to their normal soccer training, while the other half was involved in soccer training only. The plyometric training group enhanced their running (+1.7 and +3.2%) and jumping performance (+7.7%) significantly over the short period of time, while the control group did not. Furthermore, both groups increased their kicking velocity after just six weeks of training (+3.3 vs. 6.6%). The findings suggest that a short in-season 6-week sprint and jump training regimen can significantly improve explosive strength in soccer-specific skills and that these improvements can be transferred to soccer kicking performance in terms of ball speed.


#6 Effectiveness of injury prevention programs on developing quadriceps and hamstrings strength of young male professional soccer players
Authors: Daneshjoo A1, Rahnama N2, Mokhtar AH3, Yusof A4.
Reference: J Hum Kinet. 2013 Dec 31;39:115-25. doi: 10.2478/hukin-2013-0074. eCollection 2013.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916926/pdf/jhk-39-115.pdf
Summary: Muscular strength is an important factor which is crucial for performance and injury prevention in most sports. The purpose of this study was to evaluate the effects of the FIFA's Medical Assessment and Research Centre 11+ and HarmoKnee injury prevention programs on knee strength of young professional male soccer players. Thirty-six soccer players (age: 18.9 ± 1.4 years) were divided equally into three groups; the 11+, HarmoKnee and control groups. The programs were performed for 24 sessions. Hamstring and quadriceps strength was measured using the Biodex System 3 at 30°, 60° and 90° of knee flexion. The 11+ increased quadriceps strength in the dominant leg by 19.7% and 47.8% at 60°and 90° knee flexion, respectively, and in the non-dominant leg by 16%, 35.3% and 78.1 % at 30°, 60° and 90° knee flexion, respectively. The HarmoKnee group, however, showed increased quadriceps strength only at 90° i.e., by 85.7% in the dominant leg and 73.8% in the non-dominant leg. As for hamstring strength, only the 11+ group demonstrated an increment by 24.8% and 19.8% at 30° and 60° knee flexion in the dominant leg, and in the non-dominant leg, by 28.7% and 13.7% at 30° and 60° knee flexion, respectively. In conclusion, both warm-up programs improve quadriceps strength. The 11+ demonstrated improvement in hamstring strength while the HarmoKnee program did not indicate any improvement. We suggest adding eccentric hamstring components such as Nordic hamstring exercise to the HarmoKnee program in order to enhance hamstring strength.


#7 Static vs. Dynamic Acute Stretching Effect on Quadriceps Muscle Activity during Soccer Instep Kicking
Authors: Amiri-Khorasani M, Kellis E

Reference: J Hum Kinet. 2013 Dec 31;39:37-47. doi: 10.2478/hukin-2013-0066. eCollection 2013.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916919/pdf/jhk-39-37.pdf
Summary: The purpose of this study was to compare the effects of static and dynamic stretching on quadriceps muscle activation during maximal soccer instep kicking. The kicking motion of twelve male college soccer players (body height: 174.66 ± 5.01 cm; body mass: 72.83 ± 4.83 kg; age: 18.83 ± 0.75 years) was captured using six synchronized high-speed infra-red cameras whilst electromyography (EMG) signals from vastus medialis (VM), lateralis (VL) and rectus femoris (RF) were recorded before and after static or dynamic stretching. Analysis of variance designs showed a higher increase in knee extension angular velocity (9.65% vs. -1.45%, p < 0.001), RF (37.5% vs. -8.33%, p < 0.001), VM (12% vs. -12%, p < 0.018), and VL EMG activity (20% vs. -6.67%, p < 0.001) after dynamic stretching exercises. Based on these results, it could be suggested that dynamic stretching is probably more effective in increasing quadriceps muscle activity and knee extension angular velocity during the final swing phase of a maximal soccer instep kick than static stretching.


#8 Evaluation of Research Using Computerised Tracking Systems (Amisco® and Prozone ®) to Analyse Physical Performance in Elite Soccer: A Systematic Review
Authors: Castellano J, Alvarez-Pastor D, Bradley PS.
Reference: Sports Med. 2014 Feb 8. [Epub ahead of print]
Summary: Technology improvements in elite soccer have enabled the performance of individual players and teams to be analysed in extreme detail. The volume and immediate availability of this information allows coaches and sports scientists to make more informed decisions about current and future needs, thus increasing the teams' potential to perform. In the last decade, one of the most valuable technologies used in elite soccer is the Computerised video tracking system that quantifies technical and physical performance parameters, although new applications are being developed. This systematic review aims to evaluate the pertaining research literature that has specifically used the Amisco® and Prozone® Computerised video tracking systems to analyse the physical performance of elite players. MEDLINE, SPORTDiscus, PsycINFO, ProQuest, and Teseo were used for the literature search. After two selection phases, a total of 38 studies were reviewed, which revealed that the majority of studies were of a high standard with most fulfilling the majority of the quality criteria. A critical appraisal of this literature was conducted to assess issues regarding sample size, positional subsets, variables measured, and possible future applications. This systematic review demonstrates that Computerised video tracking systems are a valuable data collection tool to enable sports scientists to identify the current physical demands placed on players in competition to allow them to apply data to training and testing protocols. Current Computerised tracking systems in elite soccer still provide adequate detail on the physical and technical performances of players but must develop further to compete with the array of additional parameters offered by new technologies such as global or local positioning system technology. However, physical parameters are highly dependent on the role played by technical and tactical factors, and thus improved knowledge of these parameters is needed to allow a more complete understanding of their impact on physical demands.


#9 Measuring Acceleration and Deceleration in Soccer-Specific Movements Using a Local Position Measurement (LPM) System
Authors: Stevens T GA, de Ruiter CJ, van Niel C, van de Rhee R, Beek PJ, Savelsbergh G JP.
Reference: Int J Sports Physiol Perform. 2014 Feb 7. [Epub ahead of print]
Summary: The Local Position Measurement (LPM) system can accurately track the distance covered and the average speed of whole body movements. However, for the quantification of a soccer player's workload, accelerations rather than positions or speeds are essential. The main purpose of the present study was therefore to determine the accuracy of LPM in measuring average and peak accelerations for a broad range of (maximal) soccer-specific movements. Twelve male amateur soccer players performed eight movements (categorized in straight runs and runs involving a sudden change in direction of 90 or 180 degrees) at three intensities (jog, sub max, max). Position related parameters recorded with LPM were compared to VICON motion analysis data sampled at 100Hz. The differences between LPM and VICON data were expressed as percentage of the VICON data. LPM provided reasonably accurate measurements for distance, average speed and peak speed (differences within 2% across all movements and intensities). For average acceleration and deceleration absolute bias and 95% limits of agreement were 0.01 ± 0.36 m·s-2 and 0.02 ± 0.38 m·s-2, respectively. On average, peak acceleration was overestimated (0.48 ± 1.27 m·s-2) by LPM, while peak deceleration was underestimated (0.32 ± 1.17 m·s-2). LPM accuracy appears acceptable for most measurements of average acceleration and deceleration, but for peak acceleration and deceleration accuracy is limited. However, when the above error margins are kept in mind, the system may be used in practice for quantifying average accelerations and parameters such as summed accelerations or time spent in acceleration zones.


#10 The Physiological Response, Time-Motion Characteristics and Reproducibility of Various Speed Endurance Drills in Elite Youth Soccer Players: Small Sided Games vs Generic Running
Authors: Ade JD, Harley JA, Bradley PS.
Reference: Int J Sports Physiol Perform. 2014 Feb 7. [Epub ahead of print]
Summary: To quantify the physiological responses, time-motion characteristics and reproducibility of various speed endurance production (SEP) and speed endurance maintenance (SEM) drills. Twenty-one elite male youth soccer players completed four drills: (1) SEP 1 v 1 small-sided game (SSG), (2) SEP running drill, (3) SEM 2 v 2 SSG, (4) SEM running drill. Heart rate response, blood lactate concentration, subjective rating of perceived exertion and time-motion characteristics were recorded for each drill. The SEP and SEM running drills elicited greater (P<0.05) heart rate responses, blood lactate concentrations and subjective ratings of perceived exertion than the respective SSG's (ES: 1.1-1.4 & 1.0-3.2). Players covered less (P<0.01) total distance and high-intensity distance in the SEP and SEM SSG's compared to the respective running drills (ES: 6.0-22.1 & 3.0-18.4). Greater distances (P<0.01) were covered in high-maximum acceleration/deceleration bands during the SEP and SEM SSG's compared to the respective running drills (ES: 2.6-4.6 & 2.3-4.8). The SEP SSG and generic running protocols produced greater (P<0.05) blood lactate concentrations than the respective SEM protocols (ES: 1.2-1.7). Small-moderate test-retest variability was observed for heart rate response (CV: 0.9-1.9%), subjective ratings of perceived exertion (CV: 2.9-5.7%) and blood lactate concentration (CV: 9.9-14.4%); Moderate-large test-retest variability was observed for high-intensity running parameters (CV: >11.3%) and the majority of accelerations/deceleration distances (CV: >9.8%) for each drill. The data demonstrate the potential to tax the anaerobic energy system to different extents using speed endurance SSG's and identify SSG's elicit greater acceleration/deceleration load compared to generic running drills.


#11 Soccer Injuries in Children Requiring Trauma Center Admission
Authors: Walters BS, Wolf M, Hanson C, Mor N, Scorpio RJ, Kennedy AP Jr, Meyers JO, Coppola CP.
Reference: J Emerg Med. 2014 Feb 6. pii: S0736-4679(13)01407-8. doi: 10.1016/j.jemermed.2013.11.081. [Epub ahead of print]
Summary: Soccer continues to gain popularity among youth athletes, and increased numbers of children playing soccer can be expected to result in increased injuries. We reviewed children with soccer injuries severe enough to require trauma activation at our Level I trauma center to determine injury patterns and outcome. Our goal is to raise awareness of the potential for injury in youth soccer. A retrospective review was performed using the trauma registry and electronic medical records at a Level I trauma center to identify children (< 18 years old) treated for soccer injury from 1999-2009. Data reviewed include age, gender, mechanism, injury, procedures, and outcome. Eighty-one children treated for soccer injury were identified; 38 (47%) were male. Of these, 20 had injury severe enough to require trauma team activation and 61 had minor injury. Mean age was 14 years old (range 5-17 years, SD 2.3). Lower extremity was the most common site of injury (57%), followed by upper extremity (17%), head (16%), and torso (10%). Mechanisms were: kicked or kneed in 27 patients (33%), collision with another player in 25 (31%), fall in 18 (22%), struck by ball in 10 (12%), and unknown in 1 (1%). Procedures included reduction of fractures, splenectomy, abdominal abscess drainage, and surgical feeding access. Long hospitalizations were recorded in some cases. There were no deaths. Although less common, injury requiring prolonged hospital admission and invasive operative procedures exist in the expanding world of youth soccer. With increasing participation in the sport, we anticipate greater numbers of these child athletes presenting with serious injury.


#12 Defensive transition in soccer - are prompt possession regains a measure of success? A quantitative analysis of German Fußball-Bundesliga 2010/2011
Authors: Vogelbein M, Nopp S, Hökelmann A.

Reference: J Sports Sci. 2014 Feb 7. [Epub ahead of print]
Summary: The aim of the study was to evaluate the time required by German Bundesliga soccer teams to recover ball possession - which was operationalised as defensive reaction time - and identify both the differences between top teams and the rest of the league and the influence of match status on the aforementioned indicator. Therefore, teams were classified into 3 distinct groups according to their final league position: top, in-between and bottom. In total, all 306 games of the season 2010/2011 were analysed post-event. Top teams recovered ball possession quickest after losing it in comparison to the other groups and demonstrated lower defensive reaction times (approximately 1 s in each match status) compared to the remaining teams. Moreover, all groups showed the lowest defensive reaction times when trailing. The results of this study imply that recovering ball possession as quickly as possible after losing possession was an important determinant of successful defensive performance in German Bundesliga season 2010/2011. Further, the current score seemed to be highly influential on the defensive reaction time. The implications of the results for future research, especially considering opponent interactions, are critically discussed.


#13 Monitoring changes in VO2max via the Polar FT40 in female collegiate soccer players
Authors: Esco MR, Snarr RL, Williford HN.
Reference: J Sports Sci. 2014 Feb 7. [Epub ahead of print]
Summary: Abstract This study was conducted to determine if the Polar FT40 could accurately track changes in maximal oxygen consumption (VO2max) in a group of female soccer players. Predicted VO2max (pVO2max) via the Polar FT40 and observed VO2max (aVO2max) from a maximal exercise test on a treadmill were determined for members of a collegiate soccer team (n = 20) before and following an 8-week endurance training protocol. Predicted (VO2max and aVO2max measures were compared at baseline and within 1 week post-training. Change values (i.e., the difference between pre to post) for each variable were also determined and compared. There was a significant difference in aVO2max (pre = 43.6 ± 2.4 ml · kg · min-1, post = 46.2 ± 2.4 ml · kg · min-1, P < 0.001) and pVO2max (pre = 47.3 ± 5.3 ml · kg · min-1, post = 49.7 ± 6.2 ml · kg · min-1, P = 0.009) following training. However, predicted values were significantly greater at each time point compared to observed values (P < 0.001 at pre and P = 0.008 at post). Furthermore, there was a weak correlation between the change in aVO2max and the change in pVO2max (r = 0.18, P = 0.45). The Polar FT40 does not appear to be a valid method for predicting changes in individual VO2max following 8 weeks of endurance training in female collegiate soccer players.


#14 Effects of two recovery procedures after a football game on sensory and biochemical markers
Authors: Kawczyński A, Mroczek D, Frąckiewicz A, Chmura P, Becella L, Samani A, Madeleine P, Chmura J.
Reference: J Sports Med Phys Fitness. 2014 Feb 11. [Epub ahead of print]
Summary: The aim of this study was to investigate recovery processes on pressure pain sensitivity and blood indicators in professional football players after three different post-game training modalities: standard recovery training, no physical activity, delayed onset muscle soreness reduction training. Methods: Eleven male football field players participated in the present study. The experiment was performed in three sessions over three weeks after three football league games. The procedure was composed of the following assessments included in each session: measurement of pain pressure threshold, creatine kinase activity and myoglobin (Mb) concentration before, 24 and 48 hours after game. Results: In standard recovery training there was no full recovery in deep structure sensitivity of the frontal thigh muscles at 48 hours after game (P=0.008). In the no physical activity session, sensitivity returned to its level before game. On the contrary, in the delayed onset muscle soreness reduction training sensitivity decreased 48 hours after game (P<0.001). Creatine kinase activity decreased significantly from 24 hours to 48 hours in session with no activity and delayed onset muscle soreness reduction training (P<0.05). None of the recovery methods had an influence on Mb concentration. Conclusion: The present study points towards a potent effect of delayed onset muscle soreness reduction training on recovery after a football game.


#15 Adult female football players have higher lumbar spine and hip bone mineral density than age- and body weight-matched controls
Authors: El Hage R, Chatah R, Moussa E, Theunynck D.
Reference: J Sports Med Phys Fitness. 2014 Apr;54(2):174-8.
Summary: The aim of this study was to compare lumbar spine, total hip, femoral neck, total forearm and 1/3 Radius bone mineral density (BMD) in young female football players and age- and body weight- matched female controls (aged 18 to 30 years). Methods: This study included 18 female football players and 22 age- and body weight- matched sedentary females (aged 18 to 30 years). Weight and height were measured, and body mass index (BMI) was calculated. Daily calcium intake, daily protein intake and sleep duration were evaluated using validated questionnaires. BMD of the lumbar spine (L2-L4), the total hip (TH), the femoral neck (FN), the total forearm (TF) and the 1/3 Radius was assessed by dual-energy X-ray absorptiometry (DXA). Results: Height and BMI were not different between the two groups (football players and controls). L2-L4 BMD, TH BMD and femoral neck BMD were significantly higher in football players compared to controls (P<0.05). There were no significant differences between the two groups concerning total forearm BMD and 1/3 Radius BMD. Conclusion: This study suggests that, in young adult females, football practice is associated with an increased BMD at the lumbar spine and the total hip but not at the total forearm.